#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>

struct ListNode* reverseList(struct ListNode* head) {

    if (head == NULL)
    {
        return NULL;
    }

    struct ListNode* n1 = NULL;
    struct ListNode* n2 = head;
    struct ListNode* n3 = n2->next;

    while (n2)
    {
        n2->next = n1;
        n1 = n2;
        n2 = n3;
        if (n3)
        {
            n3 = n3->next;
        }
    }
    return n1;


}